In typical control valves, a valve cage may provide guidance for a valve plug as the valve plug moves from a closed position in which the valve plug sealingly engages a valve seat to an open position in which the valve plug is disposed away from the valve seat. When the valve is in the open position, fluid flows from a valve inlet, passes through a passage between the valve seat and the valve plug, passes through the valve cage, and exits through a valve outlet. Typically, valve cages are comprised of a plurality of disks that are arranged in a vertical stack. The disks generally have a plurality of inlet passages, at least one plenum section, and a plurality of outlet passages. In such disks, fluid enters the inlet passages, passes through the plenum sections of adjacent disks, and exits through the outlet passages. In such stacked disk valve cages, fluid exiting the outlet passages can create high noise levels that can be capable of permanently damaging the hearing of persons working close to the control valve.
To reduce the overall noise level of the fluid exiting the valve cage, a common practice is to break up flow jets into the smallest possible independent jets. Breaking up the flow jets in this manner increases the frequency of the noise generated by fluid exiting the valve cage. Typically, the peak frequency can be increased to a level that is near to or above the range that can be sensed by the human ear. Breaking up the flow jets in this manner is typically accomplished using a plurality of uniformly-sized outlet passages disposed along the outer circumference of the disks. The smaller the size of the outlet passage, the greater the attenuation of the noise. However, the smaller the size of each outlet passage, the greater the number of outlet passages that are necessary to handle the fluid passing through the valve cage. Consequently, increasing the number of outlet passages increases manufacturing costs.
Stacked disks, such as those described above, may also be used in a vent diffuser to reduce the pressure of fluid, such as steam, exiting the diffuser to the atmosphere. As is the case in valve cages, noise reduction is typically accomplished by decreasing the size, and increasing the number, of uniformly-sized outlet passages. As explained above, this decrease in size and increase in number increases the manufacturing costs of the disks.
Other types of vent diffusers may comprise a cylindrical, hollow pipe having a plurality of uniformly-sized vent apertures disposed through the wall of the pipe diffuser. To reduce the overall noise level of the fluid exiting the pipe diffuser, the size of each vent aperture is minimized to break up flow jets into the smallest independent jets possible, thereby pushing the peak frequency of the generated noise out of the audible spectrum. However, as explained above, decreasing the size of the vent apertures increases the number of necessary vent apertures, thereby increasing manufacturing costs.